Vitamin B6 deficiency cause increased excretion of

Vit B6 deficiency causes increased excretion of Xanthurenic acid.Pyridoxal phosphate is required for the synthesis of niacin from tryptophan (one vitamin is necessary for synthesis of another vitamin) (Figs17.8 and 17.9). 3-hydroxy kynurenine - 3-hydroxy anthranilic acid (Enzyme Kynureninase). Kynureninase is a PLP dependent enzyme. Hence in vitamin B6 deficiency niacin production is less. Moreover, kynurenine cannot be conveed fuher, which is metabolized to xanthurenic acid and excreted through urine. The metabolic disorders which respond to vitamin B6 therapy are xanthurenic aciduria and homocystinuria.Ref: DM Vasudevan - Textbook of Biochemistry, 6th edition, page no: 397